Research On Clear Channel Assessment For Low Power Wide Area Networks

Recently, the requirement of low power wide area (LPWA) networks is increasing rapidly, such as environmental monitoring, gas pipeline monitoring and many other infrastructure monitoring networks. With the characteristics of short and infrequent transmission, low energy consumption, low cost, and large coverage area, this kind of network has a broad application prospect in industry, agriculture, public security and military aspects. Low Energy Critical Infrastructure Monitoring (LECIM) networks are one of the most popular LPWA networks and work on the ISM bands. In IEEE802.15.4k standard, in order to avoid interference with other networks, the media access control (MAC) layer adopts carrier sensing multiple access with collision avoidance and priority channel access (CSMA/CA-PCA) algorithm, and the physical layer provides clear channel assessment (CCA) to assist MAC layer in completing the CSMA/CA-PCA. LECIM networks take advantage of spread spectrum technology to achieve a large coverage; devices in these networks should work normally in a low SNR (Signal to Noise Rate). However, researches about CCA are mainly for some specific scenarios and the LECIM networks have some differences in wireless techniques compared with current wireless networks. As a result, the classical CCA methods cannot be used for LPWA networks directly. In this thesis, we improve the classical CCA methods and propose a new CCA scheme with low complexity and energy consumption. The performance is also evaluated through Monte Carlo simulations. Our work about LECIM networks has a great significance for practical implementation.This thesis is organized as follows. Firstly, the LECIM networks and IEEE802.15.4k standard are investigated, including application scenarios, network topology, network parameters, etc. Additionally, a review about classical CCA methods, energy detection (ED), carrier sensing (CS) and hybrid detection in current wireless networks is given.Secondly, we focus on the researches about CCA for LPWA networks. To make the classical CCA methods suitable for LECIM networks, some key parameters are optimized through theoretical analysis. However, there are some drawbacks of classical CCA methods:CS holds a high reliability while power hungry and ED is power saving while less reliable. Therefore, a new CCA algorithm named by union detection (UD), which combines the advantages of ED and CS, is proposed to improve the detection performance of LECIM networks. In UD, ED works firstly. If ED could sense the busy status of channel correctly, the detection process is finished. When ED senses the idle status of channel, CS will be triggered for further identification to improve the high detection reliability.Finally, we build a simulation platform using Matlab to evaluate the performance of proposed CCA methods. Through Monte Carlo simulation results, we give conclusions that UD achieves a best trade-off between energy consumption and detection reliability and is suitable for LECIM networks.